1. Field of the Invention
This invention relates generally to methods and compositions useful for subterranean formation treatments, such as hydraulic fracturing treatments and sand control. In particular, this invention relates to use of relatively lightweight and/or substantially neutrally buoyant particles as proppant material in hydraulic fracturing treatments and as particulate material in sand control methods such as gravel packing, frac pack treatments, etc.
2. Description of the Related Art
Hydraulic fracturing is a common stimulation technique used to enhance production of fluids from subterranean formations. In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant material is injected into the formation at a pressure sufficiently high enough to cause the formation or enlargement of fractures in the reservoir. During a typical fracturing treatment, proppant material is deposited in a fracture, where it remains after the treatment is completed. After deposition, the proppant material serves to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the well bore through the fracture. Because fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore, fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment.
Hydraulic fracturing treatments commonly employ proppant materials that are placed downhole with a gelled carrier fluid (e.g., aqueous-based fluid such as gelled brine). Gelling agents for proppant carrier fluids may provide a source of proppant pack and/or formation damage, and settling of proppant may interfere with proper placement downhole. Formation damage may also be caused by gelled carrier fluids used to place particulates downhole for purposes such as for sand control, e.g., gravel packs, frac packs, etc. Formulation of gelled carrier fluids usually requires equipment and mixing steps designed for this purpose.
In the disclosed method, the application of relatively lightweight and/or substantially neutrally buoyant particulate material as a fracture proppant particulate advantageously may provide for substantially improved overall system performance in hydraulic fracturing applications, or in other well treating applications such as sand control. By xe2x80x9crelatively lightweightxe2x80x9d it is meant that a particulate has a density that is substantially less than a conventional particulate material employed in hydraulic fracturing or sand control operations, e.g., sand or having a density similar to these materials. By xe2x80x9csubstantially neutrally buoyantxe2x80x9d, it is meant that a particulate has a density sufficiently close to the density of a selected ungelled or weakly gelled carrier fluid (e.g., ungelled or weakly gelled completion brine, other aqueous-based fluid, slick water, or other suitable fluid) to allow pumping and satisfactory placement of the proppant/particulate using the selected ungelled or weakly gelled carrier fluid. For example, urethane resin-coated ground walnut hulls having a specific gravity of from about 1.25 to about 1.35 grams/cubic centimeter may be employed as a substantially neutrally buoyant proppant/particulate in completion brine having a density of about 1.2. It will be understood that these values are exemplary only. As used herein, a xe2x80x9cweakly gelledxe2x80x9d carrier fluid is a carrier fluid having minimum sufficient polymer, viscosifier or friction reducer to achieve friction reduction when pumped down hole (e.g., when pumped down tubing, work string, casing, coiled tubing, drill pipe, etc.), and/or may be characterized as having a polymer or viscosifier concentration of from greater than about 0 pounds of polymer per thousand gallons of base fluid to about 10 pounds of polymer per thousand gallons of base fluid, and/or as having a viscosity of from about 1 to about 10 centipoises. An ungelled carrier fluid may be characterized as containing about 0 pounds per thousand gallons of polymer per thousand gallons of base fluid.
Advantageously, in one embodiment use of substantially neutral buoyant particulate material may eliminate the need for gellation of carrier fluid, thus eliminating a source of potential proppant pack and/or formation damage. Furthermore, a relatively lightweight particulate material may be easier to place within a targeted zone due to lessened settling constraints, and a reduced mass of such relatively lightweight particulate material is generally required to fill an equivalent volume than is required with conventional sand control particulates, used, for example, for gravel packing purposes. Elimination of the need to formulate a complex suspension gel may mean a reduction in tubing friction pressures, particularly in coiled tubing and in the amount of on-location mixing equipment and/or mixing time requirements, as well as reduced costs. Furthermore, when treated to have sufficient strength (e.g., by substantially filling the permeable porosity of a porous particle with resin or hardener), the disclosed relatively lightweight proppant/particles may be employed to simplify hydraulic fracturing treatments or sand control treatments performed through coil tubing, by greatly reducing fluid suspension property requirements. Downhole, a much reduced propensity to settle (as compared to conventional proppant or sand control particulates) may be achieved, particularly in highly deviated or horizontal wellbore sections. In this regard, the disclosed substantially neutral buoyancy proppant/particulate material may be advantageously employed in any deviated well having an angle of deviation of between about 0 degree and about 90 degrees with respect to the vertical. However, in one embodiment, the disclosed particulate material may be advantageously employed in horizontal wells, or in deviated wells having an angle with respect to the vertical of between about 30 degrees and about 90 degrees, alternatively between about 75 degrees and about 90 degrees. Thus, use of the disclosed relatively lightweight and/or substantially neutrally buoyant particulate materials disclosed herein may be employed to achieve surprising and unexpected improvements in fracturing and sand control methodology, including reduction in proppant pack and/or formation damage, and enhancement of well productivity.
In another embodiment, protective and/or hardening coatings, such as resins described elsewhere herein may be selected to modify or customize the specific gravity of a selected base particulate/proppant material, e.g., ground walnut hulls, etc. Modification of particulate specific gravity (i.e., to have a greater or lesser specific gravity) may be advantageously employed, for example, to provide proppant or sand control particulates of customized specific gravity for use as a substantially neutrally buoyant particulate with a variety of different weight or specific gravity carrier fluids. In yet another embodiment, protective and/or hardening-type coatings may be optionally curable to facilitate proppant pack/sand control particulate consolidation after placement. In this regard, curable resins are know to those of skill in the art, and with benefit of this disclosure may be selected to fit particular applications accordingly.
The disclosed relatively lightweight and/or substantially neutrally buoyant particulate/proppant materials may be employed with carrier fluids that are gelled, non-gelled, or that have a reduced or lighter gelling requirement as compared to carrier fluids employed with conventional fracture treatment/sand control methods. In one embodiment employing one or more of the disclosed substantially neutrally buoyant particulate materials and a brine carrier fluid, mixing equipment need only include such equipment that is capable of (a) mixing the brine (dissolving soluble salts), and (b) homogeneously dispersing in the substantially neutrally buoyant particulate material.
In one embodiment, a substantially neutrally buoyant particulate/proppant material may be advantageously pre-suspended and stored in a storage fluid (e.g., brine of near or substantially equal density), and then pumped or placed downhole as is, or diluted on the fly.
In one respect, disclosed are well treating methods (e.g., hydraulic fracturing, sand control) that may be employed to treat a well penetrating a subterranean formation, and that include introducing a relatively lightweight and/or substantially neutral density particulate/proppant material into the well. Individual particles of the particulate material optionally may have a shape with a maximum length-based aspect ratio of equal to or less than about 5. Individual particles may also be optionally coated with protective materials such as resins and/or hardeners, for example, xe2x80x9c2ACxe2x80x9d phenol formaldehyde hardener from BORDEN CHEMICAL. Examples of suitable relatively lightweight and/or substantially neutrally buoyant materials for use in aqueous based carrier fluids include, but are not limited to, ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof. Optional protective coatings for coating at least a portion of individual particles of such relatively lightweight and/or substantially neutrally buoyant materials include, but are not limited to at least one of phenol formaldehyde resin, melamine formaldehyde resin, urethane resin, or a mixture thereof. Other optional coating compositions known in the art to be useful as hardeners for such materials (e.g., coating materials that function or serve to increase the elastic modulus of the material) may be also employed in conjunction or as an alternative to protective coatings, and may be placed underneath or on top of one or more protective coatings. It will be understood by those of skill in the art that such protective and/or hardening coatings may be used in any combination suitable for imparting desired characteristics to a relatively lightweight and/or substantially neutrally buoyant particulate/proppant material, including in two or more multiple layers. In this regard successive layers of protective coatings, successive layers of hardening coatings, alternating layers of hardening and protective coatings, etc. are possible. Mixtures of protective and hardening coating materials may also be possible.
In another respect, disclosed is a relatively lightweight and/or substantially neutrally buoyant fracture proppant/particulate material for use in a hydraulic fracturing/sand control treatment that is a ground or crushed walnut shell material that is coated with a resin to substantially protect and water proof the shell. Such a material may have a specific gravity of from about 1.25 to about 1.35, and a bulk density of about 0.67. In one exemplary case, size of such a material may be about 12/20 US mesh size. In another exemplary case, sizes may range from about 4 mesh to about 100 mesh. Advantageously, in some embodiments, such ground walnut shells may serve to attract fines and formation particles by their resinous nature. In one embodiment for the manufacture of such particles for proppant/sand control applications, an optional hardener may be applied to a ground walnut shell material first followed by a urethane coating as described elsewhere herein that may vary in amount as desired. For example, such a coating material may be present in an amount of from about 1% to about 20%, alternatively from about 10% to about 20% by weight of total weight of individual particles. Alternatively, such a coating material may be present in an amount of from about 2% to about 12% by weight of total weight of individual particles. Amount of resin may depend, for example, on price and application. In this regard, particulates may be first sprayed or otherwise coated with a hardener, and a coating may be applied to be about 12% by weight of total weight of the particle.
In a further embodiment, individual particles (e.g., granules) of naturally-occurring materials (e.g., made from naturally-occurring materials or derivatives of naturally-occurring materials including, but not limited to, plant-based or agricultural-based materials such as nut hulls, seed shells, processed wood materials, derivatives of such plant-based or agricultural-based materials, etc.) may be optionally treated by exposure to a modifying agent that is capable of interacting with compounds present in or on a natural material in a way that acts to increase the ability of the naturally-occurring material to resist deformation (e.g., by increasing the elastic modulus or otherwise strengthening and/or hardening the naturally-occurring material). Examples of suitable modifying agents include, but are not limited to, any compound or other material capable of modifying (e.g., crosslinking, coupling or otherwise reacting with) one or more components present in the naturally-occurring material (e.g., natural resins, lignins and/or cellulosic fibers). Specific examples of suitable modifying agents include, but are not limited to, agents including polyisocyanates, silanes, siloxanes, and combinations thereof. Selected modifying agent/s may be advantageously used to increase the elastic modulus of a given naturally occurring material, for example, to make particles of a given naturally-occurring material more suitable (e.g., having increased hardness or strength to resist or prevent deformation under downhole in situ conditions of formation temperature and formation closure stress) for use as a relatively lightweight and/or substantially neutrally buoyant fracture proppant or sand control particulate material having increased effectiveness when exposed to higher closure stresses or other mechanical stresses that may be encountered downhole during a well treatment such as a hydraulic fracturing or sand control treatment.
Effectiveness of modifying agents may be optionally enhanced, for example, by facilitating interaction between a modifying agent and one or more components present in a naturally occurring material. In this regard interaction between a modifying agent and components present in a naturally occurring material may be facilitated using one or more enhancing agents (e.g., swelling agents, penetrating agents, etc.) and/or by exposing a naturally occurring material to one or more interaction-enhancing conditions that serve to enhance interaction with a modifying agent (e.g., vacuum and/or pressure impregnation of the modifying agent into a naturally occurring material, etc.). Examples of suitable enhancing agents include, but are not limited to, liquid or gaseous ammonia, dimethyl sulfoxide (xe2x80x9cDMSOxe2x80x9d), methyl pyrrolidone, etc.
Thus, disclosed herein is a method for forming modified and strengthened particles of naturally-occurring material that may be used as relatively low density proppant or sand control particulate for fracturing or gravel packing. In one exemplary embodiment, the modifying process may include exposing particles of the naturally-occurring material to a modifying agent (e.g., that includes an aqueous mixture of alkyl silanes, such as aminopropyltriethoxy silane) to strengthen the naturally-occurring material against deformation under closure stress. The modifying agent may be exposed to the naturally-occurring materials using any suitable method, including soaking or spraying, and may be allowed to interact or react with the naturally-occurring material with or without heating. The particles of naturally-occurring material may also be optionally exposed to an enhancing agent (e.g., liquid ammonia) to allow deeper penetration and interaction of the modifying agent with components of the naturally-occurring material, thus providing more uniform crosslinking or coupling of these components with less modifying agent and also helping to minimize or avoid localized crosslinking or coupling within the particles. A coating or layer of a material such as resin or epoxy may be added after treatment with a modifying agent to further enhance or increase strength of the naturally-occurring material, and/or to minimize downhole fluid incompatibilities.
Also disclosed herein is a method of using modified particles of naturally-occurring material as a relatively lightweight particulate material that may be introduced as part of a treating fluid into a well down wellbore tubulars (e.g., tubing, workstring, casing, drillpipe) or down coiled tubing, for example at concentrations of about 0.25 to about 15 pounds per gallon of treating fluid. In one exemplary embodiment, specific gravity of the particles of modified naturally-occurring material may be about 1.3, and therefore they may be used as a substantially neutrally buoyant proppant or sand control particulate in light or heavy brines, thus eliminating the need for complex crosslinked fracturing or sand control carrier fluids.
In one embodiment, the disclosed relatively lightweight particulate/proppant material may be introduced or pumped into a well as neutrally buoyant particles in, for example, a saturated sodium chloride solution carrier fluid or a carrier fluid that is any other completion or workover brine known in the art, for example, having a specific gravity of from about 1 to about 1.5, alternatively from about 1.2 to about 1.5, further alternatively about 1.2, thus eliminating the need for damaging polymer or fluid loss material. In one embodiment, such a material may be employed as proppant/sand control particulate material at temperatures up to about 150xc2x0 F., and pressures up to about 1500 psi. However, these ranges of temperature and closure stress are exemplary only, it being understood that the disclosed materials may be employed as proppant/sand control materials at temperatures greater than about 150xc2x0 F. and/or at closure stresses greater than about 1500 psi. For example, particles of naturally-occurring material may be exposed to suitable modifying agents, with or without enhancing agents and/or conditions, in one embodiment to form relatively lightweight particulate material that may be employed as proppant or sand control particulate at temperatures up to about 300xc2x0 F., and/or at closure stresses up to about 10,000 psi, with temperatures greater than about 300xc2x0 F. and/or closure stresses greater than about 10,000 psi also being possible. In any event, it will be understood with benefit of this disclosure that core and/or layer material/s (when present) and/or interaction-enhancing materials/conditions may be selected by those of skill in the art to meet and withstand anticipated downhole conditions of a given application.
Advantageously, in one embodiment the low specific gravity of the relatively lightweight proppant material may be taken advantage of to result in a larger fracture or frac pack width for the same loading (i.e., pound per square foot of proppant) to give much larger total volume and increased width for the same mass. Alternatively, this characteristic allows for smaller volumes of proppant material to be pumped while still achieving an equivalent width.
In one respect, disclosed herein is a method for treating a well penetrating a subterranean formation, including introducing a particulate material into the well. In this method, at least a portion of the particulate material may include particles of a naturally-occurring material modified by exposure to at least one modifying agent, the modifying agent being effective to modify the naturally-occurring material by increasing the ability of the naturally-occurring material to resist deformation.
In another respect, disclosed herein is a method of fracturing a subterranean formation, including introducing a particulate material suspended in a carrier fluid into the subterranean formation at a pressure above a fracturing pressure of the subterranean formation. In this method, at least a portion of the individual particles of the particulate material may be substantially neutrally buoyant in the carrier fluid and may include particles of a naturally-occurring material modified by exposure to at least one modifying agent in an amount effective to modify the naturally-occurring material. At least a portion of individual particles of the modified naturally-occurring material may include at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof, and the modifying agent may include at least one of a silane-based compound, siloxane-based compound, polyisocyanate-based compound, or a combination thereof.
In another respect, disclosed herein is a sand control method for a wellbore penetrating a subterranean formation, including introducing into the wellbore a slurry including particulate material and a carrier fluid, and placing the particulate material adjacent the subterranean formation to form a fluid-permeable pack that is capable of reducing or substantially preventing the passage of formation particles from the subterranean formation into the wellbore while at the same time allowing passage of formation fluids from the subterranean formation into the wellbore. In this method at least a portion of the individual particles of the particulate material may be substantially neutrally buoyant in the carrier fluid and may include particles of a naturally-occurring material modified by exposure to at least one modifying agent in an amount effective to modify the naturally-occurring material. At least a portion of individual particles of the modified naturally-occurring material may include at least one of ground or crushed nut shells, ground or crushed seed shells, ground or crushed fruit pits, processed wood, or a mixture thereof, and the modifying agent may include at least one of a silane-based compound, siloxane-based compound, polyisocyanate-based compound, or a combination thereof.
In another respect, disclosed herein is a particulate composition, including particles of a naturally-occurring material modified by exposure to at least one modifying agent, the modifying agent being effective to modify the naturally-occurring material by increasing the ability of the naturally-occurring material to resist deformation.
In another respect, disclosed is a method of modifying particles of a naturally-occurring material, including exposing particles of a naturally-occurring material to an effective amount of at least one modifying agent to modify the naturally-occurring material by increasing the ability of the naturally-occurring material to resist deformation. Also disclosed are particles of modified naturally-occurring material made by this method.